Vacuum annealing of zirconium based articles

Abstract

A method of more rapidly and uniformly heating bundles of zirconium alloy tubes in a vacuum annealing furnace utilizes an induction coil to preheat the entire bundle as it is being moved into the hot zone of the furnace.

We claim: 
     
       1. A method of annealing comprising the steps of: obtaining a bundle of zirconium base alloy tubes;   placing said bundle into the cold zone of a vacuum furnace;   evacuating said cold zone and maintaining a hot zone to said furnace at a desired annealing temperature between about 820° and about 1450° F.;   moving said bundle through an energized induction coil and into the hot zone of said furnace;   heating said bundle with said energized induction coil as said bundle moves through said energized induction coil, and whereby a central tube in said bundle is heated to a temperature between about 500° F. and said desired annealing temperature, while the tubes on the periphery of said bundle are heated to a maximum temperature which is less than 50° F. above the desired annealing temperature.   
     
     
       2. The method according to claim 1 further comprising the steps of: holding said bundle within said hot zone for a predetermined period of time to provide a predetermined metallurgical structure.   
     
     
       3. The method according to claim 1 further comprising the step of: removing said bundle from said hot zone and cooling said bundle at room temperature.   
     
     
       4. The method according to claim 1 further comprising the step of removing said bundle from said hot zone and cooling said bundle to room temperature. 
     
     
       5. The method according to claim 1 wherein said desired annealing temperature is between about 870° and about 1250° F. 
     
     
       6. The method according to claim 1 wherein said maximum temperature is equal to, or less than said desired annealing temperature.